Tjahjono said it could take three weeks to download the data from the black boxes, and then six months to properly analyze it and work out what caused the plane to crash.

A still image from a video of passengers getting on the Lion Air plane before it crashed. YouTube/TVOneNews

Tjahjono was speaking a few hours before the plane's two black boxes were recovered on Thursday.

The boxes, also called flight data recorders, log plane data during a flight, and could be the the key to finding out what happened to the nearly-new Boeing 737 Max 8, which was only delivered to Lion Air a few months before it crashed.

Flight JT 610 was flying from Jakarta's Soekarno-Hatta International Airport to the city of Pangkal Pinang on the nearby Indonesian island of Bangk. It crashed around half an hour later.